Conventional uninterruptable power supplies (UPS) incorporate a primary power source (PPS) and a secondary power source (SPS) to provide switched power to a protected load device (PLD). A series of relays/contactors is typically configured between the output of the PPS and SPS to the PLD (or circuitry supplying power to the PLD) to ensure that either the PPS or the SPS is connected to the PLD. Depending on the voltage provided by and the availability of the PPS and SPS, these relays/contactors are configured to ensure that only one of the PPS/SPS is connected to the PLD. Since the relays/contactors are mechanical devices, there exists a finite transition time to ACTIVATE the relay/contactor and a finite transition time to RELEASE the relay/contactor. This is true irrespective of whether the relay/contactor is normally-OPEN or normally-CLOSED. During these ACTIVATE/RELEASE transition times, neither the PPS nor the SPS provides power to the PLD, and power necessary to support PLD operation is normally supplied by a capacitor bank placed between the relay/contactor outputs and the PLD (or circuitry supplying power to the PLD). This capacitor bank must be sized to ensure that during the ACTIVATE/RELEASE times, sufficient energy is supplied to maintain proper operation of the PLD. Since the ACTIVATE/RELEASE times may be substantial and the load presented by the PLD may be large, the size of this capacitor bank can be very large and present both a size and cost restriction on UPS power supplies using conventional relay/contactors to switch between PPS and SPS supply power.